CVE-2026-55962: TLS 1.3 post-handshake authentication: server accepts Finished without client Certificate/CertificateVerify

mediumCVSS 6.5CVE-2026-55962

CSIRTS triage

Other

What: This vulnerability allows a server to accept Finished without client Certificate/CertificateVerify in TLS 1.3 post-handshake authentication.
Who is affected: Deployments using TLS 1.3.
Urgency: Remediation is medium urgency due to the medium severity rating.
Action: Apply the fix for CVE-2026-55962.

AI-assisted analysis generated from the source advisory — verify against the original.

Details

Source: Microsoft Security Response Center (INTL · vendor-psirt · site)
Severity: medium — CVSS 6.5
Published: 2026-06-09
Exploitation: Not in CISA KEV at last sync

Original advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55962

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Low exploitation riskCVE-2026-559620.14% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 4% of all scored CVEs.

Referenced CVEs

CVE	CSIRTS overview	External
CVE-2026-55962	coverage & exploitation status	NVD · CVE.org

Same CVEs, other sources

How other CERTs, PSIRTs and databases cover the vulnerabilities in this advisory.

mediumCVE-2026-55962: TLS 1.3 post-handshake authentication (PHA) issue where a server could accept a client's Finis…nvd

Recent advisories for TLS 1.3 post-handshake authentication

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

mediumCVE-2026-55962: TLS 1.3 post-handshake authentication (PHA) issue where a server could accept a client's Finis…nvd · 2026-06-25